1. Field of the Invention
This invention relates to an ignition apparatus for an internal combustion engine, or more in particular to an ignition apparatus having a control circuit for maintaining constant the time period during which the primary current flows in the ignition coils.
2. Description of the Prior Art
Generally, a current of predetermined magnitude must be supplied to the primary winding of the ignition coils in order to apply an appropriate ignition voltage to the ignition plug of an internal combustion engine. In the event that the primary current is larger than the amount required for supplying an appropriate ignition voltage or that the current flows in the primary winding for an unnecessarily long time, a considerable amount of the current supplied from the power source of the ignition voltage is wasted. Thus, it is necessary to control at a fixed level the time during which the primary current flows. In a conventional ignition apparatus of this type, the increase in current in the power transistor at the last stage for conducting and cutting off the primary current is obstructed with an the same time controlled by negative feed back to some degree during the time which the current flows in the primary winding. Strictly speaking, however, such an apparatus does not effect any control whereby the primary current flow time is fixedly maintained, and poses a necessity for controlling the current to prevent increase thereof as well as the resulting problem of heat generated in the power transistor at the last stage. If the current flow time is constantly strictly controlled, the need for other control devices is totally eliminated, thus making it possible to obtain an ideal ignition apparatus which generates very little heat.